Nanostructure Science and Technology - World Technology ...

Appendix D. Site Reports—Japan 295
smaller sizes and with narrower size distributions than was possible with the
ionized cluster beam apparatus and are optimistic that this source can be
scaled up for much larger production than currently feasible. For example,
with the plasma sputtering apparatus, they reported production of chromium
clusters with sizes ranging between 3-4 nm with about 10% variation in size.
Previously, the average cluster size was about 8-9 nm, but with a larger
variation in size. Optimization of the helium and argon gas mixtures used in
the plasma sputtering have resulted in better control of the cluster size and
cluster size distribution, according to Prof. Sumiyama. The laser ablation
cluster source is now being developed for production of transition metal
clusters. The other two techniques, field emission and liquid metal ion
source, are not as versatile, being limited to materials that have relatively
low melting points.
Dr. Changwu Hu (Don Cox)
Dr. Hu described the efforts at Tohoku in the area of fullerene and carbon
nanotube production and characterization. Dr. Hu described three main
items:
1. chemical reaction studies of C 60 on Si(111)
2. polymerization of C 60 and C 84 by argon ion laser irradiation
3. production and characterization of single-walled carbon nanotubes
In (1), the chemical reaction of C 60 on Si(111), C 60 is deposited on
Silicon(111) and then heated to 800°C. At 800°C STM shows that a
monolayer of C 60 in registry with the Si(111) surface is covering the surface.
Upon further heating to 850°C, the C 60 layer becomes disordered. Heating
even further to 1100°C results in formation of SiC in the form of SiC
clusters of about 50 nm diameter and 2-4 nm height. This technique is
reported to be a novel low temperature route to SiC.
In (2) the fullerenes are observed by STM to polymerize upon irradiation
by an Ar ion laser and form large (150 nm diameter) clusters. Additional
studies showed that the STM pattern changed with changing bias voltage,
suggesting some polymerization is induced by the STM electric fields.
Lastly, Dr. Hu reported recent results on characterization of nanotubes
produced in the laboratory. The researchers report single-walled nanotube
yields of 20-30%, and that the diameter of the single-walled nanotube
depends on the metal used in their (metal catalyzed) production, e.g.,
nanotube radii of 0.5 nm, 0.65 nm, and 1.0 nm for Fe/Ni, Co, and La,
respectively. Raman spectroscopy and STM are used to characterize the
nanotube deposits. Attempts to interrogate the electronic structure have been
unsuccessful thus far.